1. Field of the Invention
The present invention relates to couplings and a method of manufacturing the same with which elastic deformable hoses such as a rubber hose, synthetic resin hose, etc. engage, and more particularly to the structures of the couplings and the method of manufacturing the couplings capable of preventing the hose from coming off from the coupling and capable of preventing the same hose from being broken.
2. Prior Art
A prior art tube such as a water hose or gas hose comprises a metallic coupling, a hose which engages with the metallic coupling and a fastening ring which fastens the periphery of the hose to thereby prevent the hose from coming off from the coupling.
However, such a prior art tube using the fastening ring can not completely prevent the hose from coming off from the coupling, depending on pressure applied to the hose.
To improve the above drawback, the present applicant has proposed a coupling which is disclosed in Japanese Laid-Open Patent Publication No. 3-134396 and is illustrated in FIG. 5.
In FIG. 5, three bullet-shaped projections 3 project in equal intervals from the outer periphery of a cylindrical holding portion 2 of a coupling 1 and a hose 4 formed of an elastic deformable material engages with the holding portion 2. Each of the projections 3 has a projection wall 3a. A fastening ring 5 is wound around the outer periphery of the hose 4 to fasten the hose 4.
With such an arrangement, the hose 4 is hard to come off from the coupling 1 since the fastening ring 5 hits against each projection 3.
However, it has revealed that the following problems are liable to occur in the prior art tube described above.
That is, since each end edge 3b of the projecting wall 3a is pointed, there was such a drawback that the end edge 3b broke the hose 4 as denoted at the breakage 4a from which liquid leaks during long use of the hose.